Acrylamide co-polymers are widely used in the manufacture of 100% recycled fiber paper and to re-build strength of the recycled cellulose fibers and to impart dry tensile strength to the recycled paper. An acrylamide co-polymer must have some cationic charges to be retained on the cellulose fibers. Because 100% recycled fiber contains high levels of anionic contamination, it is desirable to use highly cationic, charged glyoxalated polyacrylamides to achieve higher resin retention on the fibers and greater dry strength performance.
Cationic polyacrylamides can be obtained by co-polymerization of acrylamide monomers and cationic co-monomers such as diallyl dimethyl ammonium chloride (DADMAC). According to FDA regulations, a cationic polyacrylamide cannot incorporate more than 10% by weight DADMAC; such cationic polyacrylamides have relatively low charge density. A low charge density polymer can be blended with a polymer with a higher charge density and used to strengthen recycled paper. But because high charge density polymers have faster fiber absorption rates than low charge density compounds, the two components of the blend separate and the higher charge density component does not improve retention of the low charge density component.
There is a need in the art for paper strengthening agents with higher charge density. Such agents would be particularly suitable for strengthening 100% recycled paper and mechanical printing paper.